1. Field of the Invention
The present invention relates to a semiconductor integrated circuit having a switch cell that controls conduction and shutoff of a power supply path for supplying power to a circuit cell within a circuit block, and a switch arranging and wiring method.
2. Description of the Related Art
MTCMOS (Multi-Threshold Complementary Metal Oxide Semiconductor) technology is known as technology for controlling the shutoff of power supply to a circuit and the cancellation of the shutoff by a switch.
Generally, the threshold voltage of a transistor in a logic circuit or the like needs to be lowered as a design value in order to prevent a signal delay accompanying a decrease in power supply voltage or an element miniaturization. When the threshold voltage of a transistor in a logic circuit or the like is low, a high leakage current occurs. The MTCMOS technology prevents unnecessary consumption of power by a circuit in a stopped state by shutting off a leakage current path of the logic circuit or the like by means of a transistor (power supply switch) designed to have a higher threshold voltage than a transistor in the logic circuit or the like.
In application of the MTCMOS technology to a circuit block, internal voltage lines referred to as a so-called virtual VDD line and a so-called virtual GND line are provided within the circuit block. The internal voltage lines are connected to a global real power supply line (real VDD line) and a real reference voltage line (real VSS line) for establishing connection between blocks outside the circuit block, via a power supply switch for power shutoff and the cancellation of the shutoff.
The power supply switch is provided at three kinds of positions, that is, a position between a functional circuit that is started and stopped repeatedly and the real VDD line, a position between the functional circuit and the real VSS line, and both the positions. In general, a PMOS transistor is used as the switch on the VDD side, and an NMOS transistor is used as the switch on the VSS line side.
The starting and stopping of the functional circuit in the MTCMOS applied block is controlled by a circuit within an MTCMOS non-applied block set in an operating state at all times while supplied with power from the real VDD line and the real VSS line after the semiconductor integrated circuit is started. Alternatively, a configuration can be adopted in which a control signal for controlling the starting and stopping of the functional circuit in the MTCMOS applied block can be input from an external terminal of the semiconductor integrated circuit.
A power supply switch can be realized by a cell within an MTCMOS applied block. More specifically, within an MTCMOS applied block, one or more power supply switches may be provided for each logic circuit cell of an inverter, a NAND circuit, a NOR circuit or the like, or within a functional circuit cell realized by a few logic circuits, and a dedicated power supply switch cell without a logic circuit or a functional circuit may be provided. The switch arrangement within the MTCMOS applied block will hereinafter be referred to as an “internal switch (SW) arrangement,” and a semiconductor integrated circuit adopting the arrangement will hereinafter be referred to as an “internal SW arrangement type IC.”
As opposed to the internal SW arrangement type IC, a semiconductor integrated circuit in which power supply switches are arranged around a circuit block as an object of power supply control is known (see Japanese Patent Laid-Open No. 2003-289245 and Japanese Patent Laid-Open No. 2003-158189 (hereinafter referred to Patent Document 1), for example). A switch arrangement of this type will hereinafter be referred to as an “external SW arrangement,” and a semiconductor integrated circuit adopting the arrangement will hereinafter be referred to as an “external SW arrangement type IC.”
The external SW arrangement enables a layout policy for an “MTCMOS switch block” to be determined freely independently of a layout policy for an MTCMOS applied region (logic cell region). When the whole of the MTCMOS switch block is custom-designed, a layout that is advantageous in terms of area can be realized. Thus, the “MTCMOS switch block” is suitably used as a switch external to a circuit block having a general-purpose circuit (for example, a memory, a CPU or the like) referred to as a so-called “macro” as a part or the whole of the circuit block.